Study On The Forming Mechanism Of The Slumped Turbidite And The Controlling Sandbody Model Of High Frequency Base-level Cycle Of Dongying Delta

The abundant slumped turbidite sandbodies developing in the front of Dongying delta in Dongying depression are the important exploring object to the subtle hydrocarbon reservoir, but their forming mechanism and development rule is complex, and it is difficult to predict. Combining with the sedimentary simulating experiment and the study of high-resolution sequence stratigraphy, this paper has discussed the controlling factors of the forming of slumped turbidites and high frequent sequences, and established the controlling sandbody model of high frequency sequence, and put forward the corresponding exploring method.Based on the flume experiment, the forming process of slumped turbidite in different trigger mechanisms which include natural slumped turbidites with no trigger action and one associated with seismism and one with wave action, are simulated. The results show that compaction sinking of estuary region in front of delta is basic cause which induces slumping without trigger condition; Under seismism, there are two types slumping including liquefaction slumping and redan slumping in front of delta, and redan slumping develops first order slumping and second order slumping; Under wave action, zone liquefaction sediment traps and fingerlike sandbody of wave base above there form, and fingerlike sandbody can bring isolation slumped turbidites. Mostly the turbidites in front of delta are formed in these mechanisms together. Where the turbidites develop can be divided into four regions approximately, and each region can develop different kinds of turbidite. In general, the slumped turbidite sandbodies generated by wave action are close to main slumped body in front of delta, the slumped turbidite sandbodies with seismism distribute in a larger range, and the slumped turbidite sandbodies generated with no trigger action mostly distribute among the former two.The gyration of the tectonic subsidence and the episode of the fracture movement control the development and evolvement of the multi-grade base-level cycle of Dongying delta. The base-level falling stage is usually equivalent to the stabile stage of the sedimentary basement, during the base-level falling stage, natural slump is the mainly factor to form the slumped turbidite, and the wave is the second factor. The base-level rising stage corresponds to the active stage of the tectonic subsidence and episodic fracture movement, during the base-level rising stage, the episodic fracture movement can trigger cosmically slump, and the lacustrine wave and lacustrine current boost up. In conclusion, the turbidites mostly develop from the later base-level falling stage to the early base-level rising stage.According to the theory and correction method of the base-level cycle, four long-term and nine middle-term base-level cycle can be identified from the second stage to the third stage of Shahejie formation of Dongying delta, moreover the sedimentary facies composing and the evolvement rule has been analysed in this paper. According to analyze the inducing factors in the base-level cycle, the controlling sandbody model of high frequency base-level cycle of Dongying delta is established. During the base-level rising stage there develop large-scale turbidite fans, and during the base-level falling stage the small-scale turbidites dominate. There are apparent self-similar features on the controlling of base level to turbidites. The developing degree and scale of turbidite are affected by the progradation and katogene of delta. In plane the distribution of slumped turbidites is controlled by configuration break of slope.In view of that the turbidites develop concentration, and have small size and low exploration rate, the fine exploratory work thinking is proposed considering scale, benefit and exploratory cycle. It was applied in Niu871 region and acquired remarkable effects.